Re: [PATCH 0/4] Drop wbinvd_on_all_cpus usage

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 19/03/2022 19:42, Michael Cheng wrote:
> To align with the discussion in [1][2], this patch series drops all usage of
> wbvind_on_all_cpus within i915 by either replacing the call with certain
> drm clflush helpers, or reverting to a previous logic.

AFAIU, complaint from [1] was that it is wrong to provide non x86 implementations under the wbinvd_on_all_cpus name. Instead an arch agnostic helper which achieves the same effect could be created. Does Arm have such concept?

Given that the series seems to be taking a different route, avoiding the need to call wbinvd_on_all_cpus rather than what [1] suggests (note drm_clflush_sg can still call it!?), concern is that the series has a bunch of reverts and each one needs to be analyzed.

For instance looking at just the last one, 64b95df91f44, who has looked at the locking consequences that commit describes:

"""
     Inside gtt_restore_mappings() we currently take the obj->resv->lock, but
     in the future we need to avoid taking this fs-reclaim tainted lock as we
     need to extend the coverage of the vm->mutex. Take advantage of the
     single-threaded nature of the early resume phase, and do a single
     wbinvd() to flush all the GTT objects en masse.

"""

?

Then there are suspend and freeze reverts which presumably can regress the suspend times. Any data on those?

Adding Matt since he was the reviewer for that work so might remember something.

Regards,

Tvrtko

  
> [1]. https://lists.freedesktop.org/archives/dri-devel/2021-November/330928.html
> [2]. https://patchwork.freedesktop.org/patch/475752/?series=99991&rev=5
> 
> Michael Cheng (4):
>    i915/gem: drop wbinvd_on_all_cpus usage
>    Revert "drm/i915/gem: Almagamate clflushes on suspend"
>    i915/gem: Revert i915_gem_freeze to previous logic
>    drm/i915/gt: Revert ggtt_resume to previous logic
> 
>   drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c |  9 +---
>   drivers/gpu/drm/i915/gem/i915_gem_pm.c     | 56 ++++++++++++++--------
>   drivers/gpu/drm/i915/gt/intel_ggtt.c       | 17 +++----
>   drivers/gpu/drm/i915/gt/intel_gtt.h        |  2 +-
>   4 files changed, 46 insertions(+), 38 deletions(-)
>